Tumor grade is a system used to classify cancer cells in terms of how abnormal they look under a microscope and how quickly the tumor is likely to grow and spread. Many factors are considered when determining tumor grade, including the structure and growth pattern of the cells. The specific factors used to determine tumor grade vary with each type of cancer.
If a tumor is suspected to be malignant, a doctor removes a sample of tissue or the entire tumor in a procedure called a biopsy. A pathologist examines the tissue to determine whether the tumor is benign or malignant. The pathologist can also determine the tumor grade and identify other characteristics of the tumor cells.
Based on the microscopic appearance of cancer cells, pathologists commonly describe tumor grade by four degrees of severity: Grades 1, 2, 3, and 4. The cells of Grade 1 tumors resemble normal cells, and tend to grow and multiply slowly. Grade 1 tumors are generally considered the least aggressive in behavior. At the other end of the spectrum, the cells of Grade 3 or Grade 4 tumors do not look like normal cells of the same type. Grade 3 and 4 tumors tend to grow rapidly and spread faster than tumors with a lower grade.
Doctors use tumor grade among other factors to develop an individual treatment plan for the patient and to predict the patient's prognosis. Generally, a lower grade indicates a better prognosis, such as the chance of recovery or recurrence.
However, tumor grading systems are not always straightforward. First, the grading systems are largely based on qualitative parameters, such as the morphology of the cells. Second, grading systems are often different for different types of cancer. For example, pathologists use the Gleason system to describe the degree of differentiation of prostate cancer cells. The Gleason system uses scores ranging from Grade 2 to Grade 10. Other grading systems include the Bloom-Richardson system for breast cancer and the Fuhrman system for kidney cancer.
A single, more objective classification system is needed for determining the prognosis and treatment plan for different types of cancers.